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Thursday, 27 August 2015

Riverfly - Riverflow

Torridge in flood - note the line of
vegetation showing the submerged bank

Today was our last attempt at the August Riverfly survey.  A friend and I volunteer to survey 8 species of invertebrates in the River Torridge near Bradford Mill.  This takes place once a month between April and September.  We usually plan to survey mid-month so as to allow us an alternative date, if the weather is too bad, later in the month.

Last week the it rained heavily all of the day we had planned to survey so we postponed until our alternative on the 26th August.  I drove across the Tamar to get to the site and noted flooded fields either side of the border on the Holsworthy road which did not bode well.

Surveying on the lower river bank
Nonetheless, Barrie and I set out to our survey site which is half an hour walk from where we park the car at Bradford Church. It was wet and heavy going towards the last field where the river flows.  Going through the final wet and muddy gateway we could see what is usually a strip of Juncus in a damp hollow had become a deep tributary to the Torridge. This was too deep to pass, so we walked parallel with it to where it flowed into the main river.

What a deep raging torrent! We could see the tips of Himalayan Balsam that group on top of the river bank just breaking the flood. Our survey site was under 2 meters of fast flowing turbid water carrying large branches along with the flood.

Small Copper 
Discretion took over, a couple of pictures and we trudged back home. No chance of the waters subsiding before the end of the month meant a nil return for August. It will be interested to see how quickly the invertebrates re-colonise the river after this flood event.

The silver lining to this cloud was an early return home to find my wife excited by a new species of butterfly in the garden.  A beautifully marked Small Copper adds to our species total making it 11 for our garden this year.